Document Renesas versa3 clock generator(5P35023) bindings.

The 5P35023 is a VersaClock programmable clock generator and
is designed for low-power, consumer, and high-performance PCI
Express applications. The 5P35023 device is a three PLL
architecture design, and each PLL is individually programmable
and allowing for up to 6 unique frequency outputs.
Signed-off-by: Biju Das <biju.das.jz@bp.renesas.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20230705171000.85786-2-biju.das.jz@bp.renesas.comSigned-off-by: Stephen Boyd <sboyd@kernel.org>